Process for treating fibrous materials and products so produced



Patented May 15, 1945 PROCESS FOR TREATING FIBROUS MATE- RIALS AND PRODUCTS SO PRODUCED Leonard Smidth, New York, N. Y.

No Drawing. Application February 25, 1942, Serial No. 432,253

11 Claims.

The present invention relates in general to the treatment of fibrous cellulosic materials with synthetic resins and, in particular, to urea-formaldehyde compositions for use in impregnating fibrous cellulosic materials such as wood, textiles, paper, felts and the like, and to the materials so treated. The invention also. includes correlated improvements designed to enhance the structure, appearance and utility of such impregnated ar ticles.

This invention is a continuation-in-part of my co-pending U. 5. applications Serial Nos. 664,207 and 664,208, both filed April 3, 1933, which are continuations-in-part of my parent application Serial No. 429,202, filed February 17, 1930, and contains pertinent matter from other co-pending related U. S. applications, as for example, Ser. No. 363,397, filed May 15, 1929. In my application Serial No. 429,202 and other applications as well, I describe a process which for the first time provides clear, transparent reaction products of urea and formaldehyde which possess the proper characteristics for impregnating cellulosic materials, and which are thereafter insolubilized when subjected to heat to give fabricated articles or materials having greater strength and resistance to wear and weather than prior products impregnated with urea and formaldehyde. The composition is described as having particular use as an impregnant for fibrous cellulosic materials, for example, paper, cloth, wood, cotton and the like, and it is stated that the compositionis particularly useful for impregnating and laminating paper sheets under heat and pressure. In the process described in said prior application, urea and formaldehyde are disclosed as being reacted and combined in certain moi-ratio proportions under specified conditions of acidity and temperature, whereby a composition is formed composed of a low reaction product of urea and formaldehyde in the form of a thin solution having a neutral or near-neutral pH value.

In my application Serial No. 429,202, I disclose adding in Various ways potentially acidic substances to this .thin solution comprising a. lowreaction product of urea and formaldehyde, which substances are substantially neutral, or only slightly acid at normal or room temperatures (20 to 30 C). and do not become acid, or too acid, before being subjected to a, substantial heat treatment; but which substances upon heating to elevated temperatures, or for prolonged time, for example above 40 and up to 185 C. depending upon the substance employed, will either split off acid or become acidic in character.

The formation of such low-reaction product of urea and formaldehyde may be conducted in the presence of such potentially acidic substances if the initial reaction is carried out at relatively low temperatures, or such potentially acidic substance may be added to the low-reaction product after its formation, as desired. If a drying step is ic substance and a thin solution of said low-reaction product of urea-formaldehyde at near neutral or neutral pH values, and impregnating the cellulosic material with said solution, then heating the material, the potentially acidic substance releases an acid (or has an acidic reaction), which results in acid-catalysis of the urea-formaldehyde and polymerization of the low-reaction product to form a hard, infusible water-insoluble end-product in situ. Alternatively, the reaction may be halted at an earlier stage, through application of lesser amount of heat and pressure to form intermediate products in situ.

The difiiculty or impossibility by prior inventors in obtaining urea-formaldehyde compositions suitable for thorough impregnation of fibrous materials has been due to failure to control the extent of the reaction and the flow of the composition, or inability to control, or ascertain proper amount of various catalysts employed, or failure to correlate and control the temperatures, acidity (pH), time used in drying, etc. within required limits. By controlling the pH within proper limits, by employing the moi-ratio stated, and by using initial low reaction temperatures, 1. e. below C., I have now shown that it is possible by regulating and controlling the extent of reaction, to produce uniform low reaction products in a fluid state of low viscosity soluble in aqueous media having high penetration powers into fibrous cellulosic materials, after which impregnation the reaction may be completed in situ by simple heating.

If. in accordance with prior art practice solutions which are highly acid are employed (which acid has the effect of a large volume of catalyst), or a, heating of the initial ingredients to boiling is used, the reaction becomes very rapid or violent and viscous or gelled condensation products result, which products are unsatisfactory for impregnation purposes, as compared with my thin solution. Furthermore, by substantially neutralizing the formalin either by the addition of ammonia or by the addition of fixed alkalis and a potentially acidic substance as described, using the composition for impregnation and thereafter It is a specific object of the present invention to provide a process for treating fibrous cellulosic materials to form a water-insoluble urea-formaldehyde resin in situ in order to enhance the appearance, strength, durability and permanency of such materials.

It is a specific object of the present invention to improve the physical properties of paper by impregnating it with a resin formed in situ.

It is another object to render wood more dense, tougher and more resistant to shock and abrasion.

It is a further object to impregnate a fibrous cellulosic material, such as wood, to a substantial depth with a resin formed in situ.

It is a further specific object to provide a process of treating wood which will enable the treated wood to be laminated or veneered Without chipping, cracking and splintering.

It is another object of the invention to render fibrous cellulosic material such as textiles, paper, and the like, resistant to attack'by fungi, bacteria and insects.

It is a further object of the present invention to provide a fibrous cellulosic material impregnated with a water-insoluble urea-formaldehyde condensation product, which product is formed in situ.

Another object is to produce, for sale as such, cellulose materials including cloth, wood, paper, and other cellulosic products impregnated uniformly with fusible urea-formaldehyde reaction products, stable in storage, which materials in the hands of the purchasers may be laminated, fabricated or otherwise employed and converted by heating, and also pressure if required into infusible resin-impregnated articles and materials of commerce.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The composition of the invention accordingly comprises a low reaction product of urea and formaldehyde, combined with a potentially acidic substance, formed in the manner described in my aforesaid application Serial Number 429,202. In a preferred embodiment there is employed a composition comprising a substantially neutral, water-soluble, low reaction products of urea and formaldehyde formed by reacting formaldehyde in aqueous solution with suflicient urea to take up substantially all of the formaldehyde in the reaction mass, under mild conditions which form a thin or non-viscous solution having a low viscosity, and having combined therewith a substantially neutral potentially acidic substance capable of developing acidic properties at elevated temperatures, which properties are sufiicient to acidcatalyze, and thus further the reaction of the said low reacted urea-formaldehyde composition upon heating toform an advanced reaction product of urea and formaldehyde which is waterinsoluble and which has the novel properties and improved characteristics therein and herein stated.

In impregnating the fibrous cellulosic materials of the class described withsaid composition, the composition, because of a being in 'the form of a thin solution achieves an extraordinarily high degree of penetration. As a final step, the process includes advancing the reaction of the low reaction product of urea-formaldehyde by applying heat and in'some instances alsopressure to cause the potentially acidic substance to split of! acid or to' form an acid catalyst which advances the reaction of the urea-formaldehyde product,

and which results in the formation of a waterinsoluble advanced reaction product of ureaformaldehyde in situ. In the said preferred embodiment fibrous cellulosic materials are impregnated with the thin aqueous solution of the low reaction product of urea-formaldehyde, preferably having a pH around neutrality andcontaining a potentially acidic substance, the said solution being obtained by reacting urea and aqueous formaldehyde in the moi-ratio of about 1.25 to 2 at a pH of from 4 to 7.5 at a low temperature for a short while, adding a potentially acidic substance at any convenient time, and thereafter partially or completely drying the impregnated material at moderate or slightly elevated temperature insufiicient to cause premature hardening of the reaction mass. The impregnated material is finally subjected to increased temperature of a magnitude sumcient to activate the potentially acidic substance and thus catalyze the water-soluble urea-formaldehyde low reaction product in contact with the impregnated material to form therefrom a water-insoluble urea-formaldehyde resin in situ.

In another embodiment the cellulosic material may be treated with one of the resin-forming components for example, by treating the cellulosic material with a solution of urea, thereafter impregnatlng the cellulosic material with a quantity of formaldehyde, applying a potentially acidic substance to the material, then if desired, mildly heating and drying to form a low reaction product and thereafter heating said material to an elevated temperature to release the acid, thus advancing the reaction of the urea-formaldehyde condensation product on the treated material to form the resin in, situ.

In the foregoing embodiments the potentially acidic substances, unless the same be derived from ammonia as hereinafter described, may alternatively be added to the formaldehyde solution before initial condensation occurs, or 'to the condensate at any stage, or by combining the potentially acidic substance with the cellulosic material before or after impregnation with the several ingredients or with said low reaction product.

The expression "potentially acidic substance" as used in the specification and claims is intended to include as a class any substance which is alkaline, neutral or slightly acid at room temperatures but which will render the aldehyde-containing composition acid in reaction at an elevated temperature. As described in my co-pending U. 3. application Serial Number 429,202, this class of substances capable of yielding free hydrogen ions upon heating includes compounds formed by use of ammonia as the neutralizing urea solution or to the agent, and also various inorganic salts, acid salts, water-soluble esters and organic compounds, examples of which are hereinafter given. Ammonia or ammonium hydroxide when employed in the manner described serves to produce potentially acidic substances in the low reaction products because it apparently reacts with formic acid in the formalin solution to form ammonium formate and with aldehydes therein to form some compound not positively identified, either or both of which apparently decompose upon heating and render the composition acid. The term "impregnating" is intended to include any treatment of the fibrous material with the composition wherein complete penetration through some depth of fibers is obtained whether or not the composition penetrates slightly below the surface or completely through the material.

The expression low reaction product," as used with reference to urea and formaldehyde in the specification and appended claims is intended to include any water-soluble non-viscous product formed by reacting urea with formaldehyde, such for example, as simple addition products and condensation products of urea and formaldehyde, all of which products are either substantially neutral from the beginning or may be substantially neutralized to form quite stable liquids having low viscosities and if once dried under mild conditions will again dissolve and form low viscosity solutions in aqueous media. In contrast, the expression advanced reaction product" as used herein designates any water-insoluble urea-formaldehyde condensate or polymer resulting from carrying the reaction of urea and formaldehyde beyond such low reaction stage, thereby forming either substantially thick or viscous compositions having low-penetration values for flbrous cellulosic materials or solid final substantially infusible products.

I have shown in my earlier applications aforementioned that in forming; the "low reaction produc urea and formaldehyde are reacted in moi-ratio of greater than 1.05 mols, preferably between 1.05 and 1.40 mols of urea, per 2 mols of formaldehyde. The preferred range I have described as falling between 1.1 to 1.33 mols of urea to 2 mols of formaldehyde. Somewhat more than 1.40 mols of urea may be used if desired but special procedures must be followed. For. example, the additional urea is gradually added in small proportions to the 2 mols of formaldehyde. A product satisfactory for some purposes can be obtained in such instances even though the impregnating solution is clouded and the final product weakened by the excess urea. When using between 1.05 and 1.40 mols of urea per 2 mols of formaldehyde however, a low reaction product of urea and formaldehyde can be formed which is clear or translucent and which has the desirable properties set forth herein, making it particularly suitable as a cellulose impregnating composition.

The invention is not limited to any exact procedure for mixing the given proportions of urea and formaldehyde, as it is obvious that different methods may be employed. The following are a few examples of methods of mixing and/or reacting the urea and the formaldehyde:

1. The quantities of urea and formaldehyde to be used are mixed together all at once in aqueous solution and reacted to form the low reaction product, and the resulting solution then used as the impregnating medium for the cellulosic material.

2. Urea may be gradually added to an aqueous formaldehyde solution until any of the proportions hereinbefore given are reached and the resulting low reaction product is then combined with the cellulosic material.

3. A urea-rich-urea-formaldehyde solution is added to a formaldehyde-rich urea-formaldehyde solution or vice-versa, and the resulting solution containing the low reaction product is then combined with the cellulosic material.

4. Formaldehyde may be added to molten urea.- or a solution of urea, until the required proportion above described is reached, and the low reaction product thus formed is then combined with the cellulosic material.

The pH of the reaction mass must be carefully controlled. as hasbeen pointed out. ,At the time the present invention was made, commercial formaldehyde usually contained enough formic acid to give a pH of approximately 3.0. In order to maintain the rate of reaction between the urea and formaldehyde completely under control "the pH is preferably initially adjusted to between 5 and 7. Reactions in a mixture having 'a pH of 3, or numerically less than 3 usually go so fast as to get out of control and unavoidably the reaction advances past the low reaction stage, and in consequence the end products formed are in ferior and often worthless.

The more acidic the composition the quicker will be the curing time and hence the more it stiifens or cures on standing. In order to prevent the low reaction ,product from curing or stiffening too fast and in order to avoid the necessity of an immediate impregnation, it is most advantageous that the reaction mass, if not already so, be made neutral or only slightly acidic by adjusting the same to a pH value between 6 and 7, preferably 6.5. Although the operable range for general use is between 5.8 and 7.0, solutions may be employed having a pH range as low as 4.0 to 5.8 where the composition is to be used as formed. that is. where it is not required to stand or remain stable for any substantial period of time either before or after impregnation.

If the pH were initially adjusted to 7.0 or greater than 7.0 using fixed alkali and no potentially acidic substance added, then the composition would not cure satisfactorily for most purposes although it would be stable and would not decompose for long periods of time. The reaction between urea and formaldehyde apparently is immobilized if the mass is kept at a pH of slightly alkaline value. The use of ammonia as the neutralizing agent has an unique effect in that the pH of the product remains around neutrality so long as it is not substantially heated, but upon heatingorboiling,the ammonia compounds break down into acidic compounds and the pH is then reduced to about 6.1. Such action of the ammonia compounds prevents the composition from curing too rapidly or prematurely, or becoming too viscous or gelling during storage, thus preserving the composition as a thin so lution suitable for deep impregnation. In view of this action of ammonia it is considered, for the purposes of this invention, as falling within the class of potentially acidic substances." In contrast, fixed alkalis such as sodium or potassium hydroxide do not form compounds which liberate acid on heating in the same way as ammonia, and hence the composition does not become more acidic on heating or boiling when fixed alkalis have been used.

In addition to ammonia I have disclosed in my mentioned prior applications that other potentially acidic substances may be dissolved in the impregnating composition and that such substances, initially alkaline or substantially neutral do not become substantially acid at 'roomtemperature but upon heating break down or split off acid or produce an acid reaction, whereby the composition becomes acid thus causing the water-soluble low reaction product of urea and formaldehyde to be converted to the water-insoluble advanced reaction product, and thus,

making it possible to carry the reaction between urea and formaldehyde to anyadvanced polymerization stage as desired. Such potentially acidic substances comprise, for example, in addition to the compounds formed by the use, of ammonia as the neutralizing agent, salts of chloracetic acid, ammonium salts, other salts which hydrolyze in solution to yield free hydrogen ions as for example, zinc chloride; water-soluble esters as for example, methyl formate; and other organic compounds as for example, formamide.

I have shown that no apparent reaction liberating acid takes place when the reaction mass having ammonia as the neutralizing agent is kept at normal temperatures. At about 40 C., however, reaction commences to take place and acid is liberated, the rate of which reaction increases with the increase in temperature. Hence ammonia or ammonium hydroxide has the dual capacity of neutralizing the acid present or adjusting the pH to near-neutrality or slightly alkaline, thereby to permit control of the condensation reactiOn and at the same time of reacting with the free formaldehyde or formic acid to form a reaction product which in turn at elevated temperatures breaks down to liberate free formic acidwhich reaction product thus acts as a potentially acidic substance to catalyze the ureaformaldehyde at said elevated temperatures.

I have also pointed out in my prior application Serial Number 664,208 that when a somewhat greater proportion than 1.40 mols of urea is to be added to 2 mols of formaldehyde, the "reaction of urea and formaldehyde should be carried out at low temperatures, for example, at approximately 30 C. Apparently any greater proportion than 1.40 of urea present during boiling of a reaction mass (at 100 C.) goes to form a considerable amount of amorphous methylene urea, but when the reaction is carried out at low temperatures this does not occur and as a result a final product of suflicientstrength and stability for may purposes may be obtained.

In this connection I have also pointed out with regard to ammonia when used to neutralize the excess acidity-of the. initial formalin employed that if the reaction mixture is boiled .as prac-- ticed in the prior art, the pH will be found to in-'- crease quickly to a value of 7.7 and higher, i. e., distinctly alkaline and on further heating to become acidic, i. e., to dropto a pH of som value less than 6.1. If instead of boiling the mixture with ammonia the mixture is kept at 30 C., in accordance with the present invention and as described in the given examples, there is little I appreciable change in pH at such temperatures. With addition of ammonia to the mixture at low temperature and subsequent initial reaction at low temperature there is formed a water-soluble low reactionproduct of urea-formaldehyde comprising-a thin solution which because of its low viscosity is particularly satisfactory for impregnating purposes. Upon heating or curing the composition at higher temperatures it becomesmore acidic to yield an advanced, water- I insoluble reaction product of urea i'ormaldehyde within the structure of cellulosic material impremated therewith By way of illustrating but not by way of limiting the invention, the following examples are given:

Example I water-soluble low reaction product of low vis-. cosity suitable for use as an impregnant. Wood sheets were impregnated with this liquid until they contained 40% of the low reaction product based upon the dry weight of the sheet material and the sheets then partially dried using a cur-- rent of dry air forseveral hours at a temperature of 40 C. When sufllcient moisture was removed,

the partially dried sheet material was heated to a temperature of C. to advance the reaction of the urea and formaldehyde to form a resin in. situ and the sheets completely dried. Upon cooling, the impregnated sheet material was found to contain an infusible, water-insoluble ureaformaldehyde resin and to have only a negligibl precentage of free formaldehyde.

The sheet material was tested and found to have high wet tensile strength and high resistance to abrasion and water absorption.

Example I) proximately 30 C. for about 30 minutes asin Exampl I. At the end of 30 minutes the solution was found suitable for impregnating fibrous cellulosic materials as it had not reacted beyond a thin, low-viscosity point. Torthe composition there was then added a potentially acidic substance comprising a sodium salt of chloracetic acid. A cotton cloth was then impregnated by dipping the cloth into the composition and removing the excess by pressing. The impregnated material was then dried in a stream of air for a few hours at normal temperatures, after which time the material thus treated was subjected to a higher temperature, approximately 125 to C., and at such elevated temperature reaction continued between the urea and formaldehyde. After such treatment it was found that the impregnant had formed an infusible, waterinsoluble urea-formaldehyde reaction product in situ. The treated material had gained in tensile strength, and was found to have a high resistance to water absorption.

Example III as'zasoo sheet material then allowed to stand overnight at ordinary room temperatures. The reaction and as a result the article in the form molded without warping or delamination.

was thus conducted in situ from the beginning.

Aiter standing overnight the impregnated paper was dried at a somewhat elevated temperature such as 90 C. and then heated to a higher temperature such as 145' C., to continue the reac tion and to form a water-insoluble advanced reaction product of urea-formaldehyde in situ.

Because of'its low viscosity the composition 0! the invention is particularly adapted for impregnation of wood. The wood may be impregnated in the form of whole logs, cut timbers, boards or thin layers, as single or multiple layers.

dipping ,or by use of a pressure-tank apparatus action product of urea and formaldehyde it is subjected to elevated temperatures, -with or with;

out pressure, in the presence of a potentially acidic substance as described, to cause the urea and formaldehyde to form an advanced water luble reaction product in situ. When single layers of wood are impregnated with the composition they may be machined or worked in the l usual manner and used as planking, 'flooring, joists and flat work in general. Thin strips,-sec-- tions or veneers formed of wood'of the class-described in thicknesses varying from less than 0.01 inch to. thick sections of from 0.25 to 0.50 inches may be treated and combined in multiple layers to form such laminates as ordinary plywood,

resin-bonded plywood, ccmpregnated wood and the like.

Plywood may be or sections of wood in the composition comprising a mixture of potentially acidic subst'ance'and the water-soluble low reacted urea-formaldehyde product or by spreading the composition betweentwo or more such thin layers, and the layers then united and bonded under pressure at about 300. pounds per square inch. and at temperatures,

varying from 120 to 170 0., the resin function ing as an adhesive to form a multi-ply structure. Alternatively, the composition may be applied as a roam, which foam penetrates the surface or the wood to a lesser degreethanwhen T 5 wood may be impregnated by coating.'spraying,

formed by soaking thin strips Resin-bonded plywood may be molded by impregnating veneers, superimposing a number of them and then pressing into shape by inflating a rubber bag against the piles within a mold to .conform said plies to the shape of the mold, and

finally applying heatto set the resin in situ.- The bonding temperat f s. pressures and the time necessary to conduct successfully such aprocess varies, dependingjupon the type of wood and the 3 amount or impregnant employed. Usually resinor the type used in creosoting. After the wood is impregnated with the water-soluble low rea bonded plywood impregnated'with the composition-crane present invention is subjected to pressures ,ranging from approximately 200 to 1000 pounds per. square inch at temperatures of from 120 to 1707-0. depending upon the type of wood and the amount of impregnant used. Such resin-bonded plywood may be used in the coni r compregnated wood is formed. by impregnating single pieces of wood or such lammates, as resin-bonded plywood with the compos ruction or airplane fuselages, boats, molded helmets, wooden salad bowls, radio cabinets, auto fbodies, barrel staves and the like.

sition in manner described and then compressing wood under extremely high pressures at elevated temperatures to actually densify the .WO'Odfllld to form the water-insoluble resin in I situ. Th compregnated wood product is char- 1 acterized by being extremely hard and glossy as a result of application of pressures of from 1,000

a liquid solution is .employed. The use of foams required and at the same time where it ,isdesired to conserve space.

In forming resin-bonded plywood separate adhesive layers are not generally required but instead each ply of woodis separately impreg nated throughout and the plies superimposed and then bonded together at elevated temperature and pressure. In general higher pressures are employed so that it is possible to shape and 'the nature of the wood. i .wood may be molded and formed into curved to 10,000 pounds per square inch, depending upon Such compregnated articles as desired. Since compregnated wood is highly resistant to rupture or splintering it is aernployed. in various construction work such as boat decks, piling,,foundation timber and the like, and in such places where a wood is required that has a very hard, flint-like surface finish and which'is extremely resistant to the natural elements-such as water and moisture, as well as bacteria,'fungi and insects.

Paper in the form of single sheets or multiple sheets may be impregnated with the composition of the invention produced in the manner de- 1 scribed, by subjecting the impregnated paper to a suiliciently elevated temperature and/or pres sure to cause the composition to form a waterinsoluble advanced reaction product of urea and formaldehyde in situ. The-paper may be impregnated by coating, spraying, or dipping or the composition may be combined with the paper during manufacture.

A single sheet of paper may be impregnated with a relatively small amount to form a flexible, porous paper product, such as writing paper, pa-

per toweling, and the like whereby the tensile strength of such paper is increased withoutsubstantially detracting from the porosity or absorbent nature of the paper. Alternatively, the paper may be impregnated to a much greater extent in order to fill up the pores and form a nonporous material-useful in packaging and in simimold the multiple plies into articles having curved surfaces during the bonding operation, at which time the resin polymerizes and sets to form a hard, infusible water-insoluble product "lar; capacities where it" is desired to retain or preserve the contents of the package substantially free from atmospheric variations. Single sheets of paper treated to form a non-porous material may beemployed as temporary covers, bags and containers for preserving products against moisture, gases, insects and the like. Paper so treated is impervious to various gases, in particular mustard 'g as,1and thus may be employed in wrapping first-aid bandages, medicaments and the like, thereafter heat sealing the wrapper about the Dwk setopreservethecontentsfromgasinfiltration.

Paper may be treated in multiple layers and bonded together to form a resin-bonded paper laminate. The laminates may be formed by impregnating a plurality of individual paper sheets and thereafter applying heat and pressure to weld the layersto form a substantially rigid structure, or a plurality of such laminates may be superflcially impregnated as by coating with the composition and thereafter subjected to heat and pressure to form a thicker and heavier, laminated material. If but two or three sheets of material have the composition a mlied as a thin coating between said sheets and thereafter subjecting the sheets to less drastic heat and pressure, there Serial No. 664,208. Such molded paper productsmay be further shaped, stamped or cut to form gears, insulating sections, parts for electrical appliances, drinking cups and the like. Impresnated paper in the form of single sheets or multiple sheets may be formed into tubing by wrapping the paper on a mandrel in known manner. thereafter heating the mandrel and/or subjecting the paper to a rolling pressure at elevated temperatures to form a tube. I

Textiles as a class such for example as threads,

yarns, fabrics, belts and the like formed of natural or synthetic fibrous cellulosic materials such as linen, cotton, rayon, may be impregnated with the composition of the invention. The textile material may be impregnated as by coating, spraying, back-filling. Padding'or dipping and the like,

or flbers which may have become united by the inanymannerknowntotheart The-textile.

material is impregnated with the low viscosity water-soluble, low reaction product, preferably containing the potentially acidic substance admixture therewith. the impregnated material thereafter being subjected to a heat treatment to partially and/or completely dry the material, winch-treatment may be supplemented by further heat treatment at higher temperatures, with or without the application of pressure, to form a water-insoluble, advanced reaction product in situ.

Single l yers of textile material may be impregnated with a small percentage of the composition by weight to give a porous flexible product. Such textiles may be subjected'to elevated temperatures to form the water-insoluble resin in situ and to render the textile more resistant to creasing, crushing, shrinking and the like. For example, when the composition is applied in low concentration to a viscose rayon fabric the'low reaction product being water-soluble readily'penetrates the rayon fllaments. If the dimensions of the treated fabric are now stabilized and the fabric heated to polymerize the urea-'formalde hyde in situ. the fabric after such treatment is found to have dimensional stability and a higher production yield. I

When the various textile materials are given a full impregnation with the compoation, as by saturating the textile with a high concentration of .the water-soluble low reaction product and porous material may the composition polymerizationofthe-resin.

Single layers of textilematerial having applied thereto a heavy coating, to form anonbe used astracing cloth, window shades, glared shower curtains. tent fabric, awning material, raincoat material, gasproofedclothing and the like.- Window pane substitutes which are non-shatterproof vunder explosion or bombardment may be formed .by

knitted or netted fabric with.

treating woven,

so asto flll up the interstices to form amultiplicity of small windows between the threads, thereafter heating to form terial may be wound over a mandrel and heated to form. a molded tube. Multiple heat and pressure to form the advanced", water-- insoluble urea-formaldehyde reaction product in situ. Alternatively, one ply of fabric, may be impregnated with the composition and employed as a core for binding one or more piles of untreated tabric to form a laminated material suitable as a collar cloth. By back-filling one layer of textile fabric with the composition, applying a second untreamd' layer of material thereto, and subjecting the plurality of layers to heat and pressure tobind them together, another embodiment of a collar cloth can be To form stifler laminated fabrics or felts, a large number of plies of such textiles thoroughly impregnated with the composition and laminated and/or molded to various shapes by subjecting the material to heat and pressure. as described in my aforesaid application Serial No. 664,208. r a a .Bylaminating asmall number of plies the laminated textile material may be formed into a waterproof and gasproof cloth while retaining flexibility, whereas by impregnating and laminating a considerable number of layers of such textile material there may be formed therefrom a variety of articles such as layers or strips of bonded material, and which may be used in electrical appliances, having very high dielectric properties, high insulation value and resistance,

and which materials may be punched or fabricated into various parts for said electrical appliances. A plurality of textile laminates thus formed may be bonded together and the material cut to form various articles such as gears, bearmoldedto'form curvedbodlea' material may be bonded to plywoodor other to form non-absorbent smooth table tops subject to heavy duty and wear.

To the composition and/or fibrous cellulosic material such as paper. wood, textile and the like, before or after treatment there may be added various substances such as dyes, pigmmts. fillers, germicidal compounds, waterproofing agents,sizing agents. plasticizers, wetting agen penetrants, textile lubricants and the like at any stage, preferably to the composition before impregnating. The composition may be used for textile printing or pad dyeing of textiles and paper. Colored effects may be obtained by coloring either the cellulosic material or introducing coloring matter into the initial condensation product. Suitable flllers' such as asbestos. lithopone, china clay or talc may be introduced at any time and at any stage during the process if so desired.

Instead of urea, thiourea, melamine or substitution products of urea or thiourea and the like, may be used insofar as they-are not speciflcally limited and it is intended that such substances be included along with urea. The formaldehyde employed may be either a commercial grade in aqueous solution or in the gaseous state or in the form of a solution of anhydrous formaldehyde or in the form of polymers of formaldehyde.

Among the advantages of the process of the losic sheet materials, the steps comprising impregnating' said cellulosic material with an aqueous dispersion of a water-soluble low reaction product of urea and formaldehyde having combined therein from 1.05 to 1.40 moles of urea per 2 moles of formaldehyde and a potentially acid ammonium salt which becomes acidic at elevated temperatures between 40 and 185 0., and thereafter heating said impregnated material to cause the-potentially acid ammonium salt to become acidic and thereby advance the reaction between the urea and formaldehyde in contact with said cellulosic material to form a water-insoluble ureaformaldehyde resin in situ.

1 3. In a process'for impregnating paper, the

' steps comprising'impregnating said paper with present invention is the elimination or organic solvents usually required prior to impregnation. which solvents are often dangerous and unpleasant to handle, expensive, and usually very inflammable and explosive. Furthermore, such organic solvents ordinarily have a preferential adsorption by the cellulosic materials of the class described and consequently penetrate the. said cellulosic materials too rapidly, thus depositing a superficial layer of resin on the surface thereof instead of carrying the resinous material into the body of the cellulosic material. In contrast, my aqueous composition carries the resin into the cellulosic material to a degree of penetration not possible when employing those resins soluble in organic solvents alone.

As an additional advantage if paper is impregnated with such thin aqueous liquid composition, the liquid penetrates the paper more quickly and thoroughly and to a greater depth than if the composition were in the form of a thick. viscous solution as suggested in the prior art. Hence production of such compositions as thin liquids stable at ordinary temperatures, enables one to market and use those compositions per se for molding or laminating work.

Since certain changes in carrying out the above process may be made without departing from the scope of the invention, it is intended that all matter contained in the above deserip- 1 tion shall be interpreted as illustrative and not in a limiting sense. 7

It is also to be understood that the following claims are intended to cover-all of the generic and specific features of the inve'ntion'herein described, and all phases of the invention which,' as

an aqueous dispersion of -a water-soluble low reaction product of urea and formaldehyde having combined therein from 1.05 to 1.40moles of ureaper 2 moles of formaldehyde and'a potentially acidic substance which becomes acidic at elevated temperatures between 40 and 185 0.,

I with saidpaper to form a water-insoluble a matter of language, might be said to fall therebetween.

What I claim is: 1. In a process for impregnating fibrous cellulosic sheet materials, the steps comprising impregnating said cellulosicmaterial with anaqueous dispersion of a water-soluble low reaction product of urea and formaldehyde having comand thereafter heating said impregnated material to cause the potentially acidic substance to become-acidic and thereby advance the reaction between the urea and formaldehyde in contact ureaformaldehyde resin in situ.

4. In a process for impregnatingwood, the

steps comprising impregna'tingflsaid wood with an aqueous. dispersion of .a water-soluble low reaction product of urea andformaldehyde having combined therein from 1,05 to 1.40 moles of ureaper 2 moles of formaldehyde and a poten tially acidicv substance which becomes acidic. at elevated temperatures between 40 and 'C.,

and thereafter heating said impreg ated material to cause-the potentially -acidic substance to become acidic and-thereby advance the reaction between the urea and formaldehyde in contact with said'woqd to form'aewater-insoluble ureaformaldehyde ,resin in situ,

5;. In a process for impregnating textile material, the steps comprisingimpregnating said textile material with an aqueous dispersion of a water-soluble low reaction product of urea and formaldehyde having combined therein from 1.05

to 1.40 moles of urea per 2moles of formaldehyde and apotentially acidic substancewhich becomes acidic at elevated temperatures between 40 and 185 C.,'and thereafter heating said impregnated material to cause the potentially acidic substance to become acidic and thereb advance the reaction between the urea and formaldehyde in contact with said textilematerial to 'form a waterinsoluble urea-formaldehyde resin in situ.

6'. A, composition for impregnating fibrous cellulosic sheet materials, comprising an aqueous dispersion of a low viscosity; water-soluble, low

reaction product of urea and formaldehyde formed by reacting from 1.05 tol1.40 moles of urea per 2 moles of. formaldehyde, and a potentially acidic substance which becomes acidic at elevated temperaturesibetween 40 and 185 C.,

said potentially acidic substance" beins reactive as a catalyst at elevated temperatures between 40'- and 185' c. toadvlnce'the reaction in said urea-formaldehyde low reaction-product, therebyv 'formins a water-insoluble advanced reaction 'acid ammonium salt which becomes acidic at elevated temperatures between 40" and 18510., said potentially acid ammonium salt beins reactive as acatalyst at elevated temperatures between 40 and 185 C. to advance the reaction in said urea formaldehyde low reaction product, thereby for-min: a water-insoluble advanced reaction product of urea and formaldehyde.

8. A fibrous cellulosic sheet material impregnated with a water-insoluble urea-formaldehyde 2,376,200. --Leonard Sm'idth,

M A'rm zIALs AND PRODUCTS so PRODUCED. Disclaimer filed Aug. 20, 1948, by the patentee.

10. A fibrous cellulosic material comprising natural wood imprelnated with a water-insoluble urea-formaldehyde resin formed in situ, said resin comprising urea and formaldehyde combined in a proportion of from 1.06 to 1.40 moles of urea per 2 moles of formaldehyde.

11. A textile material impreflnated with a water-insoluble urea-formaldehyde resin formed in situ, said resin comprising urea and formaldehyde combined in a proportion of from 1.05 to so 1,40 moles of urea per 2 o es o o al h momim Disclaimer 7 New York, N. Y. vPnocriss FOR TREATING Fnmous Patent'dated May 15, 1945.

Hereby enters this disclaimer to claims 8 and 11 of said patent.

[Oflic'ial Gazette September 14,' 1.948.]

said potentially acidic substance" beins reactive as a catalyst at elevated temperatures between 40'- and 185' c. toadvlnce'the reaction in said urea-formaldehyde low reaction-product, therebyv 'formins a water-insoluble advanced reaction 'acid ammonium salt which becomes acidic at elevated temperatures between 40" and 18510., said potentially acid ammonium salt beins reactive as acatalyst at elevated temperatures between 40 and 185 C. to advance the reaction in said urea formaldehyde low reaction product, thereby for-min: a water-insoluble advanced reaction product of urea and formaldehyde.

8. A fibrous cellulosic sheet material impregnated with a water-insoluble urea-formaldehyde 2,376,200. --Leonard Sm'idth,

M A'rm zIALs AND PRODUCTS so PRODUCED. Disclaimer filed Aug. 20, 1948, by the patentee.

10. A fibrous cellulosic material comprising natural wood imprelnated with a water-insoluble urea-formaldehyde resin formed in situ, said resin comprising urea and formaldehyde combined in a proportion of from 1.06 to 1.40 moles of urea per 2 moles of formaldehyde.

11. A textile material impreflnated with a water-insoluble urea-formaldehyde resin formed in situ, said resin comprising urea and formaldehyde combined in a proportion of from 1.05 to so 1,40 moles of urea per 2 o es o o al h momim Disclaimer 7 New York, N. Y. vPnocriss FOR TREATING Fnmous Patent'dated May 15, 1945.

Hereby enters this disclaimer to claims 8 and 11 of said patent.

[Oflic'ial Gazette September 14,' 1.948.] 

